Is Thermal Grease Conductive? Insulating vs Conductive Thermal Paste Explained

A common question in electronics manufacturing is: is thermal grease conductive? The correct answer is: it depends on the formulation. Standard silicone thermal grease filled with ceramic powders such as alumina, zinc oxide or boron nitride is electrically insulating, while special silver-filled or metal-filled thermal greases are electrically conductive. Choosing the wrong type can cause short circuits - or unnecessary cost. This guide explains the difference in detail.

Why Fillers Decide Conductivity

Thermal grease consists of a silicone oil base plus thermally conductive fillers. The filler type determines both thermal performance and electrical behavior:

Standard Thermal Grease Is Insulating

Most commercial thermal pastes - including the popular 1.0-3.0 W/m·K white or grey silicone greases used for CPUs, GPUs, LED drivers and power modules - are electrically insulating. They provide a high breakdown voltage, allowing safe application on exposed circuit traces and components. Hanast insulating thermal grease grades are RoHS 2.0 compliant and non-corrosive: HN100, HN200 and HN300 offer breakdown voltage of 2450 V/mm at 0.20 mm thickness, making them safe for exposed circuitry. HN400 (4.0 W/m·K) uses low-resistance fillers and must only be applied to non-exposed, non-live surfaces, while the metal-filled HN500 and HN600 (5.0-6.0 W/m·K) deliver maximum performance for CPU/GPU and power modules but are intended for enclosed interfaces only.

When Conductive Thermal Grease Is Used

Silver-filled or metal-filled greases are used only where the highest thermal conductivity is required and electrical insulation is not needed, for example between a bare die and a metal heat spreader, or between a transistor case and its mounting base. They must be applied with care because any overflow can bridge adjacent pins or traces.

How to Check Whether a Thermal Grease Is Conductive

1. Read the technical data sheet: look for "volume resistivity" and "breakdown voltage";
2. Insulating grades typically show volume resistivity above 10¹² Ω·cm;
3. Look at color and filler: silver/copper-filled compounds are usually grey-metallic and heavier;
4. When in doubt, measure resistance across a thin cured film with a multimeter.

Safety Rules for Application

• Use insulating grease on PCBs, LED boards and crowded SMT assemblies;
• Keep conductive grease strictly inside the intended contact area;
• Never use conductive grease on aluminum heat sinks - silver particles can cause galvanic corrosion;
• For automated lines, confirm dispensing volume to avoid overflow.

Electrical Specifications to Check on the Data Sheet

For insulating grades, two values matter most: volume resistivity (typically ≥10¹² Ω·cm) and dielectric breakdown voltage (often 2-10 kV/mm depending on layer thickness). Hanast thermal grease for LED drivers and power supplies is formulated to maintain high insulation while delivering thermal conductivity of 1.0 W/m·K or more.

FAQ

Can thermal paste cause a short circuit?

Only metal-filled conductive pastes can. Ceramic-filled insulating thermal grease is safe for electronics and is the standard choice for CPU and GPU cooling.

Is white thermal grease conductive?

Most white thermal greases use alumina or zinc oxide fillers and are electrically insulating. Always verify the data sheet.

Conductivity Testing in Your Factory

If you receive thermal grease from a new supplier, perform three quick checks: measure the volume resistivity of a 1 mm film with an insulation tester, confirm the breakdown voltage stated on the data sheet, and run a 100-hour thermal aging test at the maximum operating temperature. These checks protect your production line from batch variation and from mislabeled conductive material that could create latent field failures.

Storage and Handling of Thermal Grease

Store thermal grease in sealed containers at 5-30°C, away from direct sunlight and humidity. Stir gently before dispensing if oil separation is observed. Most silicone thermal greases have a shelf life of 12-24 months when stored correctly. Never mix different brands or filler systems, because filler incompatibility can change both thermal and electrical properties.

FAQ

Is grey thermal grease conductive?

Not necessarily. Grey color can come from boron nitride or zinc oxide (insulating) as well as from metal particles. Check the data sheet rather than relying on color.

Conclusion

For the vast majority of electronics applications, electrically insulating thermal grease is the right and safe choice. Conductive greases belong only in specialist bare-die or case-mounting applications. Contact Hanast for insulating thermally conductive silicone grease with certified breakdown voltage, and get free samples for validation.